Error when flushing mail queue

We're currently evaluating Jira for purchase, and have run across a bug.

I've created several projects within Jira, and I realized that no emails were being generated when people added comments. I went back to the project settings, and assigned the "Default Notification Scheme" to the project, which has sufficient settings for our needs.

After making this change, I can see new mail messages added to the queue when the events fire.

However, the messages never clear from the queue. If I click the "Flush Mail Queue" link, the messages never leave the queue.

I can use the "Send a Test Email" message functionality successfully.

Another oddity: Only the notification generated messages refuse to send. If I create a new account, I see the Account Created message go in the queue, and if I flush the queue, it gets sent fine, but the three "Comment" messages above it are ignored.

I checked the "catalina.out" file and found a lot of error messages. Here is a snippet:

recipients.size() = 0
java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:394)
at java.lang.Integer.parseInt(Integer.java:476)
at com.atlassian.jira.mail.IssueMailQueueItem.getIssueContextParams(IssueMailQueueItem.java:151)
at com.atlassian.jira.mail.IssueMailQueueItem.send(IssueMailQueueItem.java:104)
at com.atlassian.jira.mail.MailQueueImpl.sendBuffer(MailQueueImpl.java:52)
at com.atlassian.jira.web.action.admin.MailQueueAdmin.doExecute(MailQueueAdmin.java:24)
at webwork.action.ActionSupport.execute(ActionSupport.java:116)
at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:44)
at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:113)
at webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:161)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:129)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:61)
at com.atlassian.jira.web.filters.SitemeshExcludePathFilter.doFilter(SitemeshExcludePathFilter.java:40)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.atlassian.core.security.SecurityFilter.doFilter(SecurityFilter.java:170)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.atlassian.core.security.LoginFilter.doFilter(LoginFilter.java:190)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:132)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.atlassian.jira.web.filters.AppConsistencyFilter.doFilter(AppConsistencyFilter.java:112)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at com.atlassian.jira.web.filters.EncodingFilter.doFilter(EncodingFilter.java:48)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:260)

I'll add the full error message as an attachment (it's long).